The invention relates to multifocal ophthalmic lenses. In particular, the invention provides lenses that have more than one optical power, or focal length, and a smooth transition between the zones of differing power.
As an individual ages, the eye is less able to accommodate, or bend the natural lens, to focus on objects that are relatively near to the observer. This condition is known as presbyopia. Similarly, for persons who have had their natural lens removed and an intraocular lens inserted as a replacement, the ability to accommodate is totally absent.
Among the methods used to correct for the eye""s failure to accommodate are lenses that have more than one optical power. In particular, contact and intraocular lenses have been developed in which zones of distance, near, and intermediate power are provided. These lenses are disadvantageous because they are difficult to manufacture. Additionally, the lenses do not provide a smooth transition between the zones of differing refractive power.
Attempts to provide a smooth transition between zones of differing power have been made. For example, U.S. Pat. Nos. 4,898,461 and 5,877,839 disclose the use of multiple power zones, the power of each zone varying within the zone. However, the disclosed lens is difficult to manufacture and does not provide sufficient area for any one refractive power to be effective. Therefore, a need still exists for a multifocal lens that provides a smooth transition between varying power zones.